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Gene expression profiling of long-term changes in rat liver following burn injury.

ABSTRACT: The inflammatory response initiated upon burn injury is also associated with extensive metabolic adjustments. While there is a significant body of literature on the characterization of these changes at the metabolite level, little is known on the mechanisms of induction, especially with respect to the role of gene expression. We have comprehensively analyzed changes in gene expression in rat livers during the first 7 d after 20% total body surface area burn injury using Affymetrix microarrays. A total of 740 genes were significantly altered in expression at 1, 2, 4, and 7 d after burn injury compared to sham-burn controls. Functional classification based on gene ontology terms indicated that metabolism, transport, signaling, and defense/inflammation response accounted for more than 70% of the significantly altered genes. Fisher least-significant difference post-hoc testing of the 740 differentially expressed genes indicated that over 60% of the genes demonstrated significant changes in expression either on d 1 or on d 7 postburn. The gene expression trends were corroborated by biochemical measurements of triglycerides and fatty acids 24 h postburn but not at later time points. This suggests that fatty acids are used, at least in part, in the liver as energy substrates for the first 4 d after injury. Our data also suggest that long-term regulation of energy substrate utilization in the liver following burn injury is primarily at the posttranscriptional level. Last, relevance networks of significantly expressed genes indicate the involvement of key small molecules in the hepatic response to 20% total body surface area burn injury.

SUBMITTER: Jayaraman A

PROVIDER: S-EPMC3235793 | biostudies-literature | 2009 Mar

REPOSITORIES: biostudies-literature

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Gene expression profiling of long-term changes in rat liver following burn injury.

Jayaraman Arul A Maguire Tim T Vemula Murali M Kwon Deukwoo W DW Vannucci Marina M Berthiaume Francois F Yarmush Martin L ML

The Journal of surgical research 20070828 1

The inflammatory response initiated upon burn injury is also associated with extensive metabolic adjustments. While there is a significant body of literature on the characterization of these changes at the metabolite level, little is known on the mechanisms of induction, especially with respect to the role of gene expression. We have comprehensively analyzed changes in gene expression in rat livers during the first 7 d after 20% total body surface area burn injury using Affymetrix microarrays. A ...[more]

PMID: 18755477

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Project description:BackgroundSevere trauma, including burns, triggers a systemic response that significantly impacts on the liver, which plays a key role in the metabolic and immune responses aimed at restoring homeostasis. While many of these changes are likely regulated at the gene expression level, there is a need to better understand the dynamics and expression patterns of burn injury-induced genes in order to identify potential regulatory targets in the liver. Herein we characterized the response within the first 24 h in a standard animal model of burn injury using a time series of microarray gene expression data.MethodsRats were subjected to a full thickness dorsal scald burn injury covering 20% of their total body surface area while under general anesthesia. Animals were saline resuscitated and sacrificed at defined time points (0, 2, 4, 8, 16, and 24 h). Liver tissues were explanted and analyzed for their gene expression profiles using microarray technology. Sham controls consisted of animals handled similarly but not burned. After identifying differentially expressed probe sets between sham and burn conditions over time, the concatenated data sets corresponding to these differentially expressed probe sets in burn and sham groups were combined and analyzed using a "consensus clustering" approach.ResultsThe clustering method of expression data identified 621 burn-responsive probe sets in four different co-expressed clusters. Functional characterization revealed that these four clusters are mainly associated with pro-inflammatory response, anti-inflammatory response, lipid biosynthesis, and insulin-regulated metabolism. Cluster 1 pro-inflammatory response is rapidly up-regulated (within the first 2 h) following burn injury, while Cluster 2 anti-inflammatory response is activated later on (around 8 h post-burn). Cluster 3 lipid biosynthesis is down-regulated rapidly following burn, possibly indicating a shift in the utilization of energy sources to produce acute phase proteins, which serve the anti-inflammatory response. Cluster 4 insulin-regulated metabolism was down-regulated late in the observation window (around 16 h post-burn), which suggests a potential mechanism to explain the onset of hypermetabolism, a delayed but well-known response that is characteristic of severe burns and trauma with potential adverse outcome.ConclusionsSimultaneous analysis and comparison of gene expression profiles for both burn and sham control groups provided a more accurate estimation of the activation time, expression patterns, and characteristics of a certain burn-induced response based on which the cause-effect relationships among responses were revealed.

Project description:Type of experiment: Comparison of liver samples between sham (control) and 20% TBSA (total burn surface area) burn rats collected at 1h, 4h, 8h, and 24h. Experimental factors: Burn injury and time; Experiment design: All experimental liver samples collected after 1h, 4h, 8h, and 24h after burn injury were compared to a common reference (sham control treated as 0h time point); Bio source: Sprague-Drawley male rats weighing 150-200 g supplied through Charles river laboratories, MA (www.criver.com); Bio material manipulations: Rats (n=3 for each scald-burn and sham-burn time point) were individually housed in a temperature-controlled (25oC) and light-controlled room (12h light-dark cycle) and allowed to adjust to their new surroundings for at least 5 days prior to the experiment. Water and rat chow were provided ad libitum to the animals. On the day of the treatment, the animals were randomly divided into two groups, burned and sham-burned. The burn injury consisted of a full-skin-thickness scald burn of the dorsum, calculated to be ~ 20% of the ratâs total body surface area (TBSA), induced by immersing the designated area in boiling water for 10 s [Yamaguchi, 1997 #416]. Rats were resuscitated with an intra-peritoneal injection of sterile saline solution (1.5 mL/Kg body weight/% TBSA) immediately after burn. At each time point, three animals belonging to each group was sacrificed, the serum collected, and stored at â80oC. Hybridization extract: Total RNA was isolated from approximately 50 mg of pooled liver tissue using the Nucleospin II RNA isolation kit from Clontech (Palo Alto, CA), as per the manufacturerâs instructions. Labeling protocol: Labeling was performed as instructed by Affymetrix, Inc (www.affymetrix.com). In brief, 10 Î¼g of total RNA was used for the double-stranded cDNA synthesis using the T7-oligo (dT) promoter primer kit (Affymetrix Inc.) and superscript RT II enzyme (Invitrogen). 1 Î¼g of cDNA was labeled through invitro transcription reaction using T7 DNA polymerase in the presence of biotin labeled ribonucleotides. The cRNA was cleaned up using the Qiagen RNeasy columns following manufactures instructions. The cRNA (20 Î¼g) was fragmented using the fragmentation buffer supplied as part of the Gene Chip Sample Cleanup Module (Affymetrix). Image analysis and raw data description: The images were analyzed using MAS V.0 software provided by Affymetrix, Inc. The raw data output consists of several metrices: Signal, Detection, Detection p-value, Stat pairs, Stat pairs used. Signal is a measure of the abundance of the transcript. Detection is call that indicates whether the transcript is detected (P, present), undetected (A, absent), or at the limit of detection (M, marginal). Detection p-value is a measure of the significance of the detection call. Stat pairs, is the number of probe pairs for a particular probe set on an array. Stat pairs used, is the number of probe pairs per probe set used in the analysis. Normalized and summarized data: All chips were scaled to a target intensity of 500 to account for differences between the replicate chips and their hybridization efficiencies using Affymetrix GENECHIP MAS V.0 software. The entire dataset is available at gene expression omnibus (http://www.ncbi.nlm.nih.gov/geo/) with the accession number GSE802. Three filters were serially used to obtain the list of annotated genes that demonstrated differential expression in intensity between sham and burn injured animals. In the first filter, only genes that were flagged as âpresentâ by the MAS V.0 analysis software in at least one of the time points in all replicate chips were considered for further analysis. This step eliminated all genes for which the expression data was not reproducible between the replicate chips. The genes that passed this criterion were subjected to a second filter where ANOVA was performed to test each gene independently for a statistical difference in expression between groups (0, 1, 4, 8 and 24 h). The output of the analysis is the probability (p value) that a difference in expression can be observed by chance i.e., probability of getting a false positive. While the occurrence of false positives can be controlled by choosing a higher significance level (0.01 or 0.001) it also concomitantly increases the false negatives. Therefore, in this study we have chosen to work with ANOVA p-value cut-off 0.05. To reduce the occurrence of the false positives, we have used the false discovery rate (FDR) method (33) which adjusts the ANOVA p-value (cut-off 0.05) while taking the dependencies between the genes into consideration. The 695 genes that demonstrated a significant ANOVA p-value were then selected and their expression values averaged. The third filter selected 339 genes that were either up-regulated or down-regulated by at least 2-fold between any one time point (1, 4, 8 or 24h) and the 0h time point (Sham control). To determine the temporal profiles in the data, gene expression values were hierarchically clustered using the dChip software (www.dChip.org). The expression values for a gene across all samples were standardized by setting the mean to 0 and standard deviation to 1. The software then builds a hierarchical cluster tree based on centroid-linkage method using Pearson correlation coefficient as the distance metric. A set of genes were assigned to cluster groups empirically based on visual inspection of their temporal expression patterns.

Project description:Volumetric muscle loss (VML) injuries, by definition, exceed the endogenous repair capacity of skeletal muscle resulting in permanent structural and functional deficits. VML injuries present a significant burden for both civilian and military medicine. Despite progress, there is still considerable room for therapeutic improvement. In this regard, tissue-engineered constructs show promise for VML repair, as they provide an opportunity to introduce both scaffolding and cellular components. We have pioneered the development of a tissue-engineered muscle repair (TEMR) technology created by seeding muscle progenitor cells onto a porcine-derived bladder acellular matrix followed by cyclic stretch preconditioning before implantation. Our work to date has demonstrated significant functional repair (60-90% functional recovery) in progressively larger rodent models of VML injury following TEMR implantation. Notwithstanding this success, TEMR implantation in cylindrically shaped VML injuries in the tibialis anterior (TA) muscle was associated with more variable functional outcomes than has been observed in sheet-like muscles such as the latissimus dorsi. In fact, previous observations documented a dichotomy of responses following TEMR implantation in a rodent TA VML injury model; with an ?61% functional improvement observed in fewer than half (46%) of TEMR-implanted animals at 12 weeks postinjury. This current study builds directly from those observations as we modified the geometry of both the VML injury and the TEMR construct to determine if improved matching of the implanted TEMR construct to the surgically created VML injury resulted in increased functional recovery posttreatment. Following these modifications, we observed a comparable degree of functional improvement in a larger proportion of animals (?67%) that was durable up to 24 weeks post-TEMR implantation. Moreover, in ?25% of all TEMR-implanted animals, functional recovery was virtually complete (TEMR max responders), and furthermore, the functional recovery in all 67% of responding animals was accompanied by the presence of native-like muscle properties within the repaired TA muscle, including fiber cross-sectional area, fiber type, vascularization, and innervation. This study emphasizes the importance of tuning the application of tissue engineering technology platforms to the specific requirements of diverse VML injuries to improve functional outcomes. Impact Statement This report confirms and extends previous observations with our implantable tissue-engineered technology platform for repair of volumetric muscle loss (VML) injuries. Based on our prior work, we addressed factors hypothesized to be responsible for significant outcome variability following treatment of VML injuries in a rat tibialis anterior model. Through customization of the muscle repair technology to a specific VML injury, we were able to significantly increase the frequency at which functional recovery occurred, and furthermore, demonstrate durability out to 6 months. In addition, the enhanced biomimetic qualities of repaired muscle tissue were associated with the most robust functional outcomes.

Project description:Main contributors to adverse outcomes in severely burned pediatric patients are profound and complex metabolic changes in response to the initial injury. It is currently unknown how long these conditions persist beyond the acute phase post-injury. The aim of the present study was to examine the persistence of abnormalities of various clinical parameters commonly utilized to assess the degree hypermetabolic and inflammatory alterations in severely burned children for up to three years post-burn to identify patient specific therapeutic needs and interventions.Nine-hundred seventy-seven severely burned pediatric patients with burns over 30% of the total body surface admitted to our institution between 1998 and 2008 were enrolled in this study and compared to a cohort non-burned, non-injured children. Demographics and clinical outcomes, hypermetabolism, body composition, organ function, inflammatory and acute phase responses were determined at admission and subsequent regular intervals for up to 36 months post-burn. Statistical analysis was performed using One-way ANOVA, Student's t-test with Bonferroni correction where appropriate with significance accepted at p<0.05. Resting energy expenditure, body composition, metabolic markers, cardiac and organ function clearly demonstrated that burn caused profound alterations for up to three years post-burn demonstrating marked and prolonged hypermetabolism, p<0.05. Along with increased hypermetabolism, significant elevation of cortisol, catecholamines, cytokines, and acute phase proteins indicate that burn patients are in a hyperinflammatory state for up to three years post-burn p<0.05.Severe burn injury leads to a much more profound and prolonged hypermetabolic and hyperinflammatory response than previously shown. Given the tremendous adverse events associated with the hypermetabolic and hyperinflamamtory responses, we now identified treatment needs for severely burned patients for a much more prolonged time.

Dataset Information

Gene expression profiling of long-term changes in rat liver following burn injury.

Publications

Gene expression profiling of long-term changes in rat liver following burn injury.

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